The ability to detect chemical vapors, especially volatile organic compounds (VOCs), is important in many applications including environmental monitoring and the like. Such detection and/or monitoring of organic vapors may find particular use in, for example, so called “end of service life indicators” which are desired for personal protective equipment such as respirators.
Many methods for the detection of chemical analytes have been developed including, for example, optical, gravimetric, and microelectromechanical (MEMS) methods. In particular, sensors that monitor electrical properties such as capacitance, impedance, resistance, etc., have been developed. Often, such sensors rely on the change that occurs in the electrical properties of a material upon adsorption of an analyte onto, or absorption of an analyte into, the material.
In one vapor sensor design, a layer of a polymer of intrinsic microporosity (PIM) is sandwiched between vapor impermeable electrodes held at a voltage bias, forming a capacitor. PIMs pack poorly at the molecular level, and hence are readily permeable by organic small molecules. As organic vapors accumulate (e.g., by absorption and/or adsorption) in the PIM layer they accumulate in the pores, and the dielectric constant of the material between the electrodes increases causing a change in capacitance that can be measured. However, if the electrodes are impermeable to organic vapors then there can be limited exposed surface of the PIM layer through which vapor absorption can occur.
To overcome this problem, discontinuous electrodes having openings therethrough and interdigitated electrode configurations have been used. However, it remains desirable to have sensor elements suitable for use in sensor devices for rapidly detecting organic vapors with good sensitivity.